Novel Caulobacter bacteriophages illustrate the diversity of the podovirus genus Rauchvirus

The podovirus BPP-1 is currently the only member of the Podovirus genus Rauchvirus. Here, we describe three new Caulobacter bacteriophages (Jess A, SR18, and RW) that show genetic similarity to BPP-1 but have many different genetic and structural features that differentiate them from BPP-1. Jess A and SR18 are closely related to each other and should be considered two members of a new species. They share a similar gene order with BPP-1. However, they do not appear to form lysogens or have the tropism switching mechanism that has been described for BPP-1. Bacteriophage RW also exhibits some homology to BPP-1. However, it is quite different from the other three phages, and we propose that it should be considered a representative of a third species of the genus Rauchvirus. Taken together, the differences among these four members of the genus Rauchvirus indicate that this divergent genus has a long evolutionary history and that there are many more rauchviruses waiting to be discovered.